Keratoconus (KC) is the most common corneal dystrophy in the U.S. and affects one in every 500 to 2000 Americans. This ocular condition involves progressive corneal thinning that eventually causes an outward bulging of the cornea. KC is often misdiagnosed as myopia and astigmatism. In a study of 91 patients seeking keratorefractive surgery, 5 cases (5.5%) were identified as KC from a topography examination. The onset of KC typically occurs in teenagers and adults in their 20s. The NIH/NEI Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a prospective, observational study of 1,209 KC patients whose purpose is to characterize the changes in vision, corneal curvature and scarring and quality of life of the Keratoconus patients and to better understand the variation of these measures over time. The typical age of onset of the condition, its long duration and the importance of vision to life functions increase the importance of diagnosing KC as a disease. In fact, studies have shown that the impact of KC on quality of life indicators extends far beyond what one might expect from the loss of visual acuity alone. Previously, treatment options were quite limited and usually relied upon the proper selection and constant fitting of rigid gas-permeable contact lens during the disease's progression. As a result, the advantages gained by the detection of mild or early stage form of KC, Forme Fruste Keratoconus (FFKC), were limited. However, comparatively recent developments in ophthalmic cornea treatments have altered this situation. Specifically, new treatment options now exist for FFKC and KC that suggest clear potential advantages for early diagnosis of patients. Furthermore, the increasingly popular use of LASIK and PRK makes detection of FFKC quite important to minimizing the potential of undesirable surgical outcomes. KC must be detected and quantified in the earliest stage possible to understand the disease's progression and to determine the best treatments for affected patients.
Two new treatments for Keratoconus and corneal ectasia, surgery-resulted Keratoconus, are corneal collagen cross linking with Riboflavin (C3-R) and Intacs intracornea rings. C3-R strengthens the corneal integrity by cross-linking the collagen fibrils together using Riboflavin. It has successfully halted, and in some cases even reversed, KC progression when performed during early stages of the disease. Intacs corneal inserts or implants are a minimally invasive surgical option wherein two tiny, clear crescent-shaped pieces of a plastic polymer are inserted into the cornea. Intacs flatten the steep part of cornea area, correct the myopic refractive error and reduce vision distortion. These treatments are especially advantageous because no cornea tissue is removed and there is no ablation or incision across the visual axis. Since these two new methods can stop or slow the progression of the disease and both provide improved visual function, early methods of detecting FFKC are more important than ever.
The existence of KC and FFKC is known to be a significant concern and most likely a contraindication for certain cornea surgery methods, such as LASIK. The Cataract and Refractive Surgery Today journal has reported several high profile lawsuits filed by FFKC patients who experienced bad outcomes following laser cornea surgery. As the popularity of laser cornea surgery increases, it is advantageous to be able to detect FFKC and early-stage KC to reduce or eliminate such surgical complications. Currently, pre-surgery LASIK patients typically undergo a clinical examination by a medical professional for indications of KC. These clinical methods include retinoscopy, slit lamp examination, indirect opthalmoscope, and handheld keratoscope. A second type of examination that uses corneal surface imaging systems is also utilized. Common cornea surface imaging instruments include Orbscan II, Humphrey Atlas, EyeSys, and Tomey TMS-4. Even with these detection methods, short-comings exist for accurate and sensitive detection of FFKC that limit the opportunities for confident clinical and large-population FFKC screening.
Around the world, experienced physicians are aware of the irregular retinal reflex appearances from high-order ocular aberrations, including KC, which may be observed using hand-held photorefractive retinoscopes. Prior to computerized testing methods such as autorefraction, the retinoscope was the main method for objective measurement of refractive error and identification of irregular astigmatism. Shortcomings of current retinoscopes include the broad-spectrum of the light sources used that integrates chromatic aberration in the measurement and the visible irradiation that stimulates pupil response and hence, in a non-mydriatic examination, reduces the examined pupillary area. Furthermore, current retinoscopic observations cannot be stored in digital form for discussion and sharing.
Photorefraction (PR) is a technique that shares similar optical features with retinoscopy but does not use a beam splitter. Photorefraction techniques can be used to create a retinal reflex image that depends upon the optical properties of the eye. However, current photorefraction techniques create poor quality images of the retinal reflex that cannot be used to detect high-order aberrations such as astigmatism which are quite common. Thus, Current PR refractive diagnostics typically produce poor readings and results and the PR technique is currently only utilized for eccentrically illuminated detection of refractive errors.
Therefore, what is needed is a new method of identifying high-order ocular aberrations such as FFKC and early-stage KC to help avoid laser cornea surgery complications and to offer the best treatment options for the largest number of individuals having these aberrations.